Modulating surface chemisorbed oxygen of cobalt-doped In2O3 microspheres for ppb-level formaldehyde detection

Abstract

Developing high-performance formaldehyde sensors is crucial for safeguarding human health, given formaldehyde's prevalence as a hazardous indoor volatile organic compound. However, formaldehyde sensors have struggled to meet demand in terms of operating temperature, selectivity, and detection limits, especially for ppb-level formaldehyde detection. Herein, Co-doped In2O3 microspheres were synthesized by solvothermal methods combined with hydrolysis methods. The introduction of heterovalent cobalt metal can generate more oxygen vacancies of In2O3, enriching its surface active sites and optimizing its surface chemisorbed oxygen, thus effectively enhancing the formaldehyde sensing performance. The experimental results show that Co doping significantly enhances the formaldehyde sensing performance of In2O3, in which the optimal Co-doped In2O3 ratio (S2) based sensor exhibits an exceptionally high response (Ra/Rg = 1342 ± 64) to 100 ppm formaldehyde at 90 ℃, about 13.8 times greater than the pure In2O3-based sensor. Additionally, it features a rapid response (≈ 2 s), excellent selectivity, and an ultralow detection limit of 10 ppb. The enhanced formaldehyde detection performance primarily arises from cobalt's catalytic activity, the increase in specific surface area, and the increase in oxygen vacancies, which optimize the surface chemisorbed oxygen.